Mechanical Technology Grade 12 NSC June 2022 Memo (English)

Downloaded from hlayiso.com SENIOR CERTIFICATE EXAMINATIONS/ NATIONAL SENIOR CERTIFICATE EXAMINATIONS MECHANICAL TECHNOLOGY: WELDING AND METALWORK 2022 MARKING GUIDELINES MARKS: 200 These marking guidelines consist of 19 pages. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 2 DBE/2022 SC/NSC – Marking Guidelines QUESTION 1: MULTIPLE-CHOICE QUESTIONS (GENERIC) 1.1 A (1) 1.2 B (1) 1.3 C (1) 1.4 D (1) 1.5 A (1) 1.6 C (1) [6] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 3 DBE/2022 SC/NSC – Marking Guidelines QUESTION 2: SAFETY (GENERIC) 2.1 Rated speed of a grinding wheel:  Because the wheel could burst/break if it turns faster than its revolution range. / Avoid an accident.   Effectiveness of the grinding process will be compromised.  (Any 1 x 1) (1) 2.2 Safety precautions of a band saw in operation:  Never leave the band saw unattended.   Use a push stick when cutting.   Hold the work piece firmly and flat on the table.   Don’t adjust the machine while working.   Don’t open any guard while the machine is on.   Make relief cuts before cutting tight curves.   Don’t force the material into the blade.   Keep hands clear from the action point.   Keep hands braced against the table.   Keep your hands on either sides of the blade and not in line with the cutting line and the blade.   Keep loose clothing clear from action point.  (Any 2 x 1) (2) 2.3 Stages in which first aid is applied:  Examination   Diagnosis   Treatment  (3) 2.4 Causes of accidents:  Unsafe acts   Unsafe conditions  (2) 2.5 TWO advantages of the product layout:  Handling of material is kept to a minimum.   Time period of manufacturing cycle is less.   Production control is almost automatic.   Control over operations is easier.   Greater use of unskilled labour is possible.   Less total inspection is required.   Less total floor space is needed per unit of production.  (Any 2 x 1) (2) [10] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 4 DBE/2022 SC/NSC – Marking Guidelines QUESTION 3: MATERIALS (GENERIC) 3.1 Tempering: Tempering is a process generally applied to steel to relieve the strains/brittleness/improve ductility  induced during the hardening process.  (2) 3.2 Annealing:  To relieve internal stresses  that may have been set up during working of metal.  To soften steel  in order to facilitate the machining process.  To refine their grain structure.   Reduce brittleness.   Make the steel ductile.  (Any 3 x 1) (3) 3.3 Normalising temperature:  Above  higher/upper critical temperature   Above  AC3 line.  (Any 1 x 2) (2) 3.4 Spark pattern for carbon steels: 3.4.1 High-carbon steel  (1) 3.4.2 Low-carbon steel / Mild steel  (1) 3.4.3 Cast-iron  (1) 3.5 Carbon diagram: A. Temperature range / °C  B. AC3 line / Higher/upper critical temperature line  C. AC1 line / Lower critical temperature line  D. Carbon content / % carbon  (4) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 5 DBE/2022 SC/NSC – Marking Guidelines QUESTION 4: MULTIPLE-CHOICE QUESTIONS (SPECIFIC) 4.1 A (1) 4.2 C (1) 4.3 A (1) 4.4 A (1) 4.5 A (1) 4.6 C (1) 4.7 D (1) 4.8 D (1) 4.9 D (1) 4.10 C (1) 4.11 C (1) 4.12 B (1) 4.13 A (1) 4.14 D (1) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 6 DBE/2022 SC/NSC – Marking Guidelines QUESTION 5: TERMINOLOGY (TEMPLATES) (SPECIFIC) 5.1 Template machine tools:  Planer   Circular saw   Drilling machine   Jig saw   Sanding machine   Shears for cutting cardboard   Any other appropriate machine tools.  (Any 4 x 1) (4) 5.2 Roof truss: A. Purlin  B. Rafter  C. Bracing member  D. Main tie / Tie beam  E. Gusset plate  (5) 5.3 Welding Symbol:     40 - 90 6 Arc   (6) 5.4 Supplementary symbols: 5.4.1  (1) 5.4.2  (1) 5.4.3 M  (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 7 DBE/2022 SC/NSC – Marking Guidelines 5.5 Steel ring material: Mean Ø  Outside Diameter  plate thickness    600  30  570 mm  Mean circumference  π  meanØ  π  570   1790,71 mm OR   1791 mm (5) [23] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 8 DBE/2022 SC/NSC – Marking Guidelines QUESTION 6: TOOLS AND EQUIPMENT (SPECIFIC) 6.1 Manual guillotine: A – Spring loaded down pedal/Foot pedal  B – Cutting table  C – Pressure plate/Blade guard  (3) 6.2 Tap wrenches:  T- handle / Double handle tap wrench.   Single handle tap wrench/Ratchet tap wrench.  (2) 6.3 Angle grinders:  Cutting   Grinding   Polishing   Sanding  (Any 3 x 1) (3) 6.4 Advantages of Inverter: Inverters are able to weld a wider variety  of materials  than conventional AC welding machines. (2) 6.5 Spot welding:  Does not use consumable electrodes   Efficient   Quick welding process   Ideal for mass production   Cost effective   Ideal for lightweight/thinner material   It can be used on a variety of metals   Ensure uniform joints  (Any 2 x 1) (2) 6.6 MIG welding procedures:  Forehand   Perpendicular   Backhand  (3) 6.7 Plasma cutting: Plasma cutting is a process that cuts through electrically conductive  material by means of an accelerated jet  of hot plasma.  (3) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 9 DBE/2022 SC/NSC – Marking Guidelines QUESTION 7: FORCES (SPECIFIC) 7.1 Steel framework: 7.1.1 Space diagram: SCALE: 10 mm = 1 m 300 N 300 N 100 mm  B Tie  30° 30° D Strut  Strut  A C NOTE: The sequence of Bow’s notation can start in any position, but must maintain clockwise rotation. 600 N (7) 7.1.2 Vector diagram: a SCALE: 1 mm = 10 N   b  d   c MEMBER MAGNITUDE BD 510 N  CD 590 N  AD 590 N  NB: Marker must redraw the diagrams according to the given scale. When marking, use a tolerance of ±2 mm. (8) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 10 DBE/2022 SC/NSC – Marking Guidelines 7.2 Stress and Strain: 7.2.1 Cross sectional area: Area   π D 2  d2  4     π 0,06  0,05 2 2  4  8,64  10 4 m 2  (3) 7.2.2 Stress: Force/Load Stress  Area 500   8,639  10 4   578770,6911 Pa  0,58 MPa  (3) 7.2.3 Strain: Stress E Strain Stress Strain   E 578770,6911   90  10 9   6,43  10 6  (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 11 DBE/2022 SC/NSC – Marking Guidelines 7.3 Moments: 40 N 60 N 50 N/m 5m 3m UDL A B C 13 m RL RR FIGURE 7.3 7.3.1 Reactions at LR and RR: Calculate LR Take moments about RR ΣRHM  ΣLHM    LR  13  250  10,5  40  8   60  3   2625 + 320 + 180 3125  13 LR  240,38 N  Calculate RR Take moments about LR ΣLHM  ΣRHM    RR  13  60  10  40  5   250  2,5   600 + 200 + 625 1425  13 RR  109,62 N  (8) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 12 DBE/2022 SC/NSC – Marking Guidelines 7.3.2 BENDING MOMENTS: BMA  240,38  2,5    600,95 Nm  BMB  240,38  5   250  2,5    1201,90  625  576,90 Nm  BMC  240,38  10  250  7,5   40  5    2403,8  1875  200  328,80 Nm  (6) 7.3.3 BM diagram: SCALE: 1 mm = 10 Nm 2,5 m 2,5 m 5m 3m A B C RR RL 600,95 Nm  576,90 Nm   328,80 Nm   0 0 NB: Marker must redraw the diagrams according to the given scale. (6) [45] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 13 DBE/2022 SC/NSC – Marking Guidelines QUESTION 8: JOINING METHODS (INSPECTION OF WELDS) (SPECIFIC) 8.1 Weld gauge: To check:  angle of preparation.   weld alignment.   fillet weld leg length/dimensions.   excess weld metal.   fillet weld throat.   undercut.   for porosity.  (Any 4 x 1) (4) 8.2 Causes of welding defects: 8.2.1 Incomplete penetration:  Too low welding current/amperage   Too slow travel speed   Incorrect torch angle   Insufficient root gap   Poor edge/joint preparation   Excessive root gap   Too fast travel speed   Too large electrode diameter   Arc length too long   Wet/contaminated electrodes  (Any 2 x 1) (2) 8.2.2 Welding spatter:  Disturbance in the molten weld pool   Too low welding current/amperage   Too high welding current/amperage   Arc length too long   Wet/contaminated electrode   Wrong polarity   Arc length too short   Incorrect type of electrode used   Incorrect included angle   Too fast travel speed   Surface contamination   Erratic wire feeding  (Any 2 x 1) (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 14 DBE/2022 SC/NSC – Marking Guidelines 8.3 Prevention of welding defects: 8.3.1 Porosity:  Cleaning the welding surface   Ensuring that arc welding electrodes are dry   Do not welding in a windy condition   Insufficient root gap   Ensure that the shielding gas supply is not interrupted   Use correct type of electrode   Reduce arc distance/length   Reduce arc travel speed  (Any 2 x 1) (2) 8.3.2 Undercutting:  Maintain correct arc travel speed.   By raising arc voltage.   Using a leading electrode/torch angle.   Reduce arc length  (Any 2 x 1) (2) 8.4 Types of flames: 8.4.1 Neutral flame  (1) 8.4.2 Carburising flame  (1) 8.4.3 Oxidising flame  (1) 8.5 Weld craters:  Formed at the end of a weld run when the electrode  is removed too soon.   Not allowing enough filler  material to fill the crater.   Having  a too big/erratic  weaving action.  (Any 1 x 3) (3) 8.6 Nick-break test:  Make a hacksaw cut at both edges, through the center of the weld.   Place specimen on two supports/bench vice.   Use a sledgehammer to break the specimen in the area of the cuts.  Inspect the exposed weld metal in the break  for incomplete fusion, slag inclusion (or other welding defects).  (5) [23] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 15 DBE/2022 SC/NSC – Marking Guidelines QUESTION 9: JOINING METHODS (STRESSES AND DISTORTION) (SPECIFIC) 9.1 Elastic deformation: It is the ability of a joint/material to return to its original position/dimensions  after the stresses have been relieved.  (2) 9.2 Shrinkage on steel: It is a form of plastic deformation where the metal has deformed  as a result of contraction on cooling.  (2) 9.3 Distortion: 9.3.1 Transverse shrinkage  (1) 9.3.2 Longitudinal shrinkage  (1) 9.4 Effects of shrinkage: 9.4.1 Electrode size:  Larger electrode size  requires higher current and causes higher welding temperature  that causes more deformation / shrinkage.  Smaller electrode size  requires lower current and causes lower welding temperature  that causes less deformation / shrinkage. (Any 1 x 2) (2) 9.4.2 Welding speed:  Decreased  welding speed tends to increase localised heat that increases distortion.   Increased  welding speed tends to decrease localised heat that decreases distortion.  (Any 1 x 2) (2) 9.5 Disadvantages of using jigs: It increases  internal stresses  in the welded joint because the metal’s movement is restricted.  (3) 9.6 Carbon composition of steels: 9.6.1 Tool steel:  0,71 – 1,5%  (1) 9.6.2 Spring steel:  0,31 – 0,70%  (1) 9.6.3 Mild steel:  0,07 – 0,30%  (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 16 DBE/2022 SC/NSC – Marking Guidelines 9.7 Quenching mediums:  Water   Oil   Brine (salt and water)   Molten metal salts   Sand   Air   Ash   Lime   Molten lead   Infused nitrogen air  (Any 2 x 1) (2) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 17 DBE/2022 SC/NSC – Marking Guidelines QUESTION 10: MAINTENANCE (SPECIFIC) 10.1 Insufficient lubrication: Pedestal drill:  Rusting of components will occur   Movement between parts will be affected   Excessive wear and seizure of moving parts   Excessive heat generation  (Any 3 x 1) (3) 10.2 Overloading on a bench grinding machine:  Resulting in malfunction of the machine   Excessive wear and reduction of machine lifespan   Damage to grinding wheel   Damage to bearing on shaft   Damage to workpiece  (Any 3 x 1) (3) 10.3 General maintenance guidelines:  The machine should be tested for correct operation.  All guards must be in place and serviceable.   The machine must be securely fixed to the floor.   All bolts, nuts and grub screws must be in place and tight.   The machine must be in a clean condition.   Lubrication points should be serviced.   All moving parts should move freely.  (Any 2 x 1) (2) [8] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 18 DBE/2022 SC/NSC – Marking Guidelines QUESTION 11: TERMINOLOGY (DEVELOPMENTS) (SPECIFIC) 11.1 Transformers: Transformers are used to connect  ducting sections  of dissimilar shapes  to each other. (3) 11.2 Hopper: 400 D C 4 3 200 1 2 VH=500 700 A B 700 11.2.1 Square to rectangular  hopper off  centre (2) 11.2.2 True length A-2:    A  2  500  400  5002 2 2  250000  160000  250000   812,4 mm  (5) 11.2.3 True length B-2:    B  2  500  300  5002 2 2  250000  90000  250000   768,11 mm  (5) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 19 DBE/2022 SC/NSC – Marking Guidelines 11.3 Truncated cone: 11.3.1 True length: A- B: π D A B   12 π  920   12  240 , 85 mm  241 mm  (3) 11.3.2 True length: 0-1: π D 0 1   12 π  860   12  225 , 15 mm  225 mm  (3) [21] TOTAL: 200 Copyright reserved